Gastrointestinal hormones are major regulators of the digestion and metabolism of food. Cholecystokinin, probably the most important of these hormones, regulates the exocrine and endocrine pancreas, gallbladder contraction, GI motility, and in addition, is a major neuropeptide. This proposal will continue work characterizing the receptors for CCK and other GI hormones. Specific aims or projects include: 1) purification of the CCK receptor and generation and characterization of antibodies directed against the receptor; 2) characterization of the biosynthesis, processing, and turnover of the CCK receptor. The role of receptor glycosylation in maturation and function will be probed. The regulation of receptor biosynthesis and degradation by CCK and other hormones will be evaluated; 3) the role of distinct receptor affinity states in initiating biological responses will be evaluated using CCK analogy active on only one affinity state; 4) the cellular uptake and processing of CCK will be determined by electron microscope autoradiography and HPLC. Cellular uptake and recycling of the CCK receptor will also be evaluated; 5) other GI hormone receptors particularly for the pancreatic polypeptide peptide, PYY, NPY family will be characterized by ligand binding and cross-linking. The localization of receptors for these and other hormones in intact tissues such as the pancreas and stomach will be evaluated by autoradiography; 6) the mRNA coding for GI hormone receptors will be characterized by expression in Xenopus oocytes. Techniques developed for the CCK receptor mRNA will be extended to other Ca2+ mobilizing receptors. Other receptors will be characterized in oocytes by their electrophysiological effects on endogenous or exogenously inserted ion channels. These projects in total will extend our understanding of the molecular structure and function of GI hormone receptors and the action of GI hormones as physiological and pathophysiological regulators.